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Best auto guide speed on the Atlas EQ-G ?

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#1 Al Miller

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Posted 24 March 2009 - 04:05 PM

I'm using the StarShoot autoguider with the Atlas EQ-G and wonder if there is a "best" or recommended speed setting for autoguiding. Thew Atlas has five: 1.125x, 1.25x, 1.5x, 1.75x, and 2.0x the siderial rate. Right now I'm using the default rate but, wonder if another choice would be better. Looking for any other thoughts and/or experiences with this.

#2 DonR

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Posted 24 March 2009 - 05:25 PM

I use pulse guiding rather than ST4 guiding, but the idea of variable guide rates is to match the guide rate with the FOV and resolution of your guiding telescope and camera. Pulse guiding systems usually have a similar parameter. If you're using the ST80 and Neximage, that's a moderately short guidescope combined with a small sensor with small pixels, resulting in about 4 arc-seconds/pixel resolution. Don't know what telescope and camera you're imaging with, but your guiding setup achieves moderately high resolution, so I would think somewhere in the middle of the range would work fine.

Raising the guide rate will cause the mount to react more quickly to guiding signals, and is most useful when using short focal length and/or low resolution in the guide scope and camera. Conversely, lowering the guide rate is most useful when using long focal length and/or high resolution in the guide scope/camera. Your setup is in between the extremes. I guide with 900mm focal length and a Meade DSI-C, resulting in about 3 arc-seconds/pixel, and I keep the pulse guiding rate at 1.5X sidereal.

#3 Al Miller

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Posted 24 March 2009 - 08:15 PM

Don,
My typical imaging scopes are the 110ED (770mm FL, f/7), or the C8 at f/6.3 (1280mm FL). Majority of the time it's the 110ED. The only CCD I use right now is the DSI II Pro or its color version. Either way the chip size is the same. My guider is always the SSAG on the ST80, 400mm, f/5.

#4 DonR

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Posted 24 March 2009 - 09:51 PM

OK, sounds good. Didn't notice the SSAG in your signature. Resolution is a little better than the Neximage and I'm sure sensitivity is much better. I would still stick with a middle value, like 1.5X.

I guess you're using PHD software for guiding. If you don't have it already, download the latest version (1.10.0) from
http://www.stark-labs.com. There's a new feature that lets you graph the corrections made by PHD in real time. Read the short section in the Help screen about it, and experiment with different guide rates. The graph may reveal an obvious benefit for a particular speed.






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